A paper additive which imparts the color and pattern of granite has been disclosed in Japanese Patent Application Disclosure HEI 2-18049, which relates to an application filed by the present applicant, wherein are illustrated inorganic or organic materials including, for example, colored or colorless inorganic powders such as active carbon powder, black coal powder, coke powder, natural graphite powder, iron oxide powder, etc. and colored synthetic resin powders of nylon, vinyl chloride resin, thermosetting epoxy resin, acryl resin, polyester resin, etc.
In addition, as paper which incorporates paper additives produced by separating printed paper into scale-like bits and scattering them into the surface layer of paper or multilayered paperboard, pattern paper which exhibits a pattern of characters, numerals, symbols, etc. (Japanese Utility Model Law Application Disclosure SHO 63-162900) and pattern paper wherein a water-resistant coating the main component of which is a natural resin or the like is coated onto the surface of the printed portion of paper containing printed characters, etc. and then the bit of paper is scattered in water and incorporated into the paper material dispersion for the surface layer of the paper or paperboard (Japanese Patent Application Disclosure SHO 64-40697) are publicly known.
However, when the decorative paper which exhibits a color and pattern imparted by a paper additive incorporated therein and disclosed in the above mentioned Japanese Patent Application Disclosure HEI 2-18049 is used as a hot-pressed form, the following problems result.
(1) During a 5 hour boiling test in hot water, an uncountable number of blisters appeared, and the occurrence of these blisters were clearly a result of the use of the paper additive.
(2) The kinds of paper additives which may be used are limited, and thus the selection of colors and patterns is restricted. Particularly, because of the relationship between the specific gravities, anti-coagulating properties and paper manufacturing yields of various coloring materials, it has been difficult to exhibit two or more colors as a pattern of spots with a uniform particle size.
Furthermore, when the design paper disclosed in the above mentioned Japanese Utility Model Law Application Disclosure SHO 63-162900 which exhibits a color and pattern imparted by printed paper cut into scale-like bits and incorporated therein is used as a hot-pressed form, the following problems result.
(3) If the scale-like printed paper bits are not added just prior to making the paper, then the color and pattern become blurred due to unraveling of the fibers, and even if added just prior to making the paper, the color and pattern blur due to stirring for dispersion.
(4) Particularly, when further grinding is done in order to make the pattern of granite from the scale-like printed paper bits, the major part thereof cannot maintain the scale-like form, and becomes flocculent or fibrous. Also, even the portion which maintains the scale-like form exhibits fraying of the fibers, and when the bit of paper is immersed and stirred in water, the scale-like form cannot be maintained, making it impossible to exhibit a uniform granite pattern.
Furthermore, concerning the pattern paper disclosed in the above mentioned Japanese Patent Application Disclosure SHO 64-40697, only the printed portion of the scattered printed paper is coated with the water-resistant coating, and therefore the other uncoated portions become frayed into a fibrous state during scattering in the paper making process, while the periphery of the coated portions also become frayed. This printed paper is of a size which allows the original characters or symbols, etc. to be read, that is, for example, about 2-2.5 cm after scattering, but with a method whereby only such printed portions are coated with a water-resistant coating and dispersed in a paper making liquid, when the purpose is granite-like spots of diameter a few .mu.m to a few mm such as according to the present invention, the spotted pattern thus obtained becomes blurred at the edges, and if the spots are particularly small, the spots themselves become difficult to distinguish, and even if used to form granite spots, natural-looking granite spots cannot be obtained. Also, if paper which is printed and coated in this manner is mechanically preground as in the case of the present invention, the portions not coated with the water-resistant coating are not sufficiently ground, and it cannot be subjected to classification treatment, making it impossible to use it by any method for the purpose according to the present invention.